Polyurethane and polyisocyanurate rigid foams suitable for roofing insulation

ABSTRACT

Polyurethane foams having a NFPA 101 Class B rating (ASTM E-84) which pass the FM 4450 Calorimeter Test are produced by reacting: (a) an organic polyisocyanate, (b) at least one polyether polyol or polyester polyol with a nominal hydroxyl functionality of at least 2.0, (c) a blowing agent composition and (d) at least one halogen-free flame retardant. The blowing agent composition includes: (1) no more than 10% by weight, based on total weight of the foam-forming composition, of one or more hydrocarbons having an LEL less than 2% by volume in air, and/or (2) a hydrocarbon having an LEL greater than 2% by volume in air, and (3) up to 1% by weight, based on total weight of foam-forming composition, of water.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/633,312, filed Oct. 2, 2012.

FIELD OF INVENTION

The present invention relates to flame retardant rigid polyisocyanurateand polyurethane foams (collectively referred to herein as“polyurethane(s)”), compositions for the production of such foams inwhich no halogenated flame retardant is included, and to processes forthe production and use of such flame retardant polyurethane foams. Thefoams of the present invention meet the criteria for an NFPA 101 LifeSafety Code designation as Class B performance in accordance with therequirements of ASTM E-84 (American Society of Testing Materials),“Standard Test Method for Surface Burning Characteristics of BuildingMaterials” and also meet the criteria for Class 1 designation underFactory Mutual's FM 4450 standard, “Approval Standard for Class 1Insulated Steel Deck Roofs”.

BACKGROUND OF THE INVENTION

Halogenated flame retardants are used in rigid polyurethane foaminsulation to ensure compliance with various flammability test protocolsrequired by national, state, and local building code agencies.Halogenated flame retardants provide a cost-effective, efficient meansto address performance criteria that have been made more difficult bysubstitution of hydrocarbon blowing agents for chlorofluorocarbons(CFC's), hydrochlorofluorocarbons (HCFC's), and expensivehydrofluorocarbons (HFC's).

Prior to concerns about the ozone depletion potential or global warmingpotential of halogenated blowing agents that had been commonly used inrigid foam insulation materials, it was relatively easy to obtain aClass A rating in ASTM E-84, “Standard Test Method for Surface BurningCharacteristics of Building Materials” by simply using a halogenatedblowing agent.

Under ASTM E-84, the test material must have a flame spread index (FSI)of 25 or less and a smoke-developed index (SDI) of 450 or less to attaina NFPA 101 Life Safety Code Class A designation. To attain a NFPA 101Life Safety Code Class B designation under ASTM E-84, the test materialmust have a FSI less than or equal to 75 and an SDI of 450 or less.

The NFPA 101 Life Safety Code Class designations for ASTM-84 should not,however, be confused with the Class A, B, or C designations for ASTME-108, “Standard Test Methods for Fire Tests of Roof Coverings”.

ASTM E-108 is a test designed to determine the resistance of an entireroof assembly, not just the foamed plastic, to an external fire fromthree perspectives—spread of flame, intermittent flame, and burningbrand. Foams used for insulation and roof coverings applied to a steeldeck require only flame spread testing.

Although only a Class B E-84 rating is generally needed for foamedplastic insulation for an insulated steel deck assembly to meet the ASTME-108 requirements of section 1505.1 of the International Building Code(IBC), steel deck assemblies insulated with rigid polyurethane foam alsomust pass the more severe Factory Mutual Roof calorimeter portion of FM4450. An FM 4450 designation of Class 1 for an insulated steel roof deckassembly means that the deck assembly meets Factory Mutual's criteriafor internal fire resistance, wind uplift, live load resistances,corrosion of metal parts, and fatigue of plastic parts. Generally, foamformulation plays a significant role in passing the combustibilityperformance requirement of the test standard while the foam manufacturerproduct specifications and installation procedures determine if the roofassembly meets the other requirements of the FM 4450 standard. It wouldbe expected that a rigid foam product that meets the combustibilityrequirement should readily obtain a Class 1 rating since it is wellknown in the industry how to properly specify and install the product. ARoof calorimeter is used to test for internal fire resistance. It isdesirable to pass FM 4450 Roof calorimeter testing without using eithera thermal barrier between the insulation and the steel decking of the 4½ft×5 ft. (1.37 m×1.52 m) mock roofing assembly or a protective coverboard on top of the insulation layer of the assembly. The Roofcalorimeter test measures fuel contributions from combustible materials(e.g., asphalt) from the deck to the fire underneath it by simulating afire inside a building. The net fuel contribution cannot exceedpredetermined maximum values as a function of time.

The ASTM E-84 Tunnel test method provides a comparative evaluation offlame spread and smoke generation for 24 feet (7.3 m) long by 20 inch(50.8 cm) wide samples placed horizontally in a tunnel furnace andexposed to a gas flame that provides 5000 Btu/min of heat. This methodwas originally developed and published by Underwriters Laboratories asUL 723 in 1950 and adopted by ASTM as a formal test method in 1961.There is a specified draft flow to move the flame front toward the endof the tunnel during the 10 minute test period and the values measuredfor flame spread and smoke levels are indexed to those obtained for theconditioned red oak flooring calibration standard, whose flame frontreaches the end of the specimen after 5½ minutes. For rigid foamsamples, a rapid initial spread of flame to the specimen's maximum valuein the first 60 seconds followed by a recession of the flame front isoften observed. Since the test method requires that the maximum distanceof flame travel be used in the calculation, the flammability of gaseousblowing agents and their concentration in the foam play a significantrole in rigid foam performance in this test.

Halogenated organophosphorus flame retardants in combination withhalogenated blowing agents have historically been used to produce foamsexceeding an NFPA 101 E-84 Class B rating in this test. These ratingsare presumably due to phosphorus acting predominantly in the condensedphase to produce a char barrier and the halogen acting as a radicalscavenger in the vapor phase.

Use of more flammable hydrocarbon blowing agents has necessitated foamformulation changes. Generally, the formulation change has been toincrease the level of halogenated organophosphorus flame retardant inthe rigid foam.

Recent concerns about human health effects and the environmental impactof polybrominated diphenyl ethers (PBDEs) led California to passlegislation imposing a state-wide ban on these types of brominated flameretardants in 2003 and prompted Great Lakes Chemical Corporation tovoluntarily phase out manufacture and importation of PBDEs into the U.S.in 2004. Subsequently, all halogenated flame retardants have come undergreater public scrutiny and increased regulatory pressure.

Tris (2-chloroethyl) phosphate (TCEP) is no longer produced in Europeand may soon be banned in Canada from some household products andmaterials based on the Canadian government's Proposed Risk AssessmentApproach for TCEP published in 2009.

A European Risk Assessment for the common flame retardant tris(2-chloro-1-methylethyl) phosphate (TCPP) that was published in 2008concluded that currently no need exists for “further information and/ortesting and no need for risk reduction measures beyond those which arebeing applied already” with regard to human health and safety.Nonetheless, a number of studies measuring levels of halogenatedorganophosphorus flame retardants in consumer products and householddust have since appeared in peer-reviewed journals.

Consequently, efforts to develop rigid polyurethane foam products thatare free of halogenated blowing agents and halogenated flame retardantsthat meet the flammability requirements for NFPA 101 Life Security CodeClass B ratings in ASTM E-84 testing and pass the FM 4450 Roofcalorimeter test have increased.

In 1994, Nicola and Weber published the results of their evaluation ofpentane, isopentane, and cyclopentane as blowing agents for use in theproduction of laminated boardstock rigid foam at the 35^(th) AnnualPolyurethane Technical/Marketing Conference in a paper entitled“Hydrocarbon Blown Foams for U.S. Construction Applications.” In thisstudy, water was used as a co-blowing agent to minimize the pentanelevel. Chloroalkyl phosphate esters and brominated aromatic phthalateesters were used in combination with the water/pentane blowing agent tomake polyisocyanurate rigid foam at a 240 index. These foams attained aClass A rating but did not meet key requirements for roofingapplications in the Factory Mutual Roof calorimeter test (FM 4450). Whenthe foam formulations were adjusted to meet this roofing requirement byincreasing the index to 300, none of the tested samples were free ofhalogenated flame retardant.

Singh et al disclose a system for the production of rigid foam thatmeets NFPA 101 Class A rating in accordance with ASTM E-84 in U.S. Pat.No. 6,319,962. The Singh et al system includes an organicpolyisocyanate, a polyfunctional isocyanate-reactive composition, lessthan about 1% by weight (based on total weight of the system) of waterin combination with a hydrocarbon blowing agent, and at least onehalogen-substituted phosphorus material. The halogen must be present atno more than 1.4% by weight of the total reactive system and thephosphorus is present at 0.3% to 2% by weight of the total reactivesystem.

Patent application U.S. 2006/0100295 describes an all liquidfoam-forming system for rigid polyurethane foam that includes at leastone liquid isocyanate or polyisocyanate, at least one aromatic polyesterpolyol, at least two halogenated flame retardants and water. The foamformed from this system has a density of at least 5 pounds per cubicfoot (pcf) (80 kg/m³) and an ASTM E-84 Class A rating.

U.S. Pat. No. 4,797,428 broadly discloses that a rigid flame retardantfoam having a Class A rating is formed as the reaction product oforganic polyisocyanate, an isocyanate-reactive mixture composed of 25%to 75% of an oligoester that is the reaction product of a dicarboxylicacid semi-ester and an alkylene oxide, and a blowing agent. Onlyhalogenated compounds are disclosed as blowing agents/flame retardantsin the patent and patent examples.

Not one of the above-described disclosures teaches a process orfoam-forming composition for the production of a rigid polyurethane foamfree of added halogens that performs as a NFPA 101 Class B foam in ASTME-84 and that also passes the FM 4450 Roof calorimeter test protocol.

U.S. Patent Application 2009/0156704 discloses rigid foam compositionsthat include halogen-free alkyl aryl phosphate esters as flameretardants in combination with mixtures of hydrocarbon blowing agentsand water. The foams produced from these compositions are classified asB2 or “normal combustibility” in accordance with DIN 4102.

To meet the criteria for B2 in DIN 4102, the average maximum flamespread of 5 specimens measuring 90 mm×190 mm cannot exceed 150 mm duringthe 20 second test after exposure to a 20 mm flame from a small burnerfor the first 15 seconds of the test. Obviously these conditions differmarkedly from those required for the ASTM E-84 Tunnel Testing describedabove.

There is no correlation between performance in DIN 4102 B2 andperformance in ASTM E-84. No claims are made that the rigid foam systemsdisclosed in U.S. Patent Application 2009/0156704 meet both the NFPA 101Class B E-84 standard and the Class 1 FM 4450 standard.

U.S. Patent Application 2009/0247657 describes improvement of thethermal stability of polyurethane-modified polyisocyanurate foam bycombining high molecular weight ammonium polyphosphate with halogenatedand non-halogenated flame retardants in the foam formulations. However,thermal stability is only determined by thermogravimetric analysis offoam samples in nitrogen, which has little bearing on performance uponexposure to a flaming ignition source such as in ASTM E-84.

U.S. Pat. No. 5,776,992 teaches that properly blended mixtures ofnitrogen-containing and nitrogen-free polyols in combination withammonium polyphosphate can produce foams with a B2 classification in theDIN 4102 test while either polyol type used separately with the flameretardant is classified as B3. There is no teaching or suggestion thatthese systems meet the Class B E-84 standard or that roof assembliescomposed of rigid foams made with these systems will pass FM 4450.

Consequently, a need still exits for a rigid polyurethane foam systemthat does not include a halogenated flame retardant or a halogenatedblowing agent and will pass both ASTM E-84 with a NFPA 101 Class Brating and FM 4450 Roof calorimeter testing.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a foam-formingcomposition which when reacted forms a rigid polyurethane foam having aNFPA 101 Class B rating (ASTM E-84) that passes the FM 4450 Roofcalorimeter test and does not include a halogenated flame retardant or ahalogenated blowing agent.

It is also an object of the present invention to provide a process forthe production of a rigid polyurethane foam having a NFPA 101 Class Brating (ASTM E-84) that passes the FM 4450 Roof calorimeter test from afoam-forming system that does not include a halogenated flame retardantor a halogenated blowing agent.

It is a further object of the present invention to provide rigidpolyurethane foams having a NFPA 101 Class B rating (ASTM E-84) thatpass the FM 4450 Roof calorimeter test and do not include a halogenatedflame retardant or a halogenated blowing agent.

These and other objects which will be apparent to those skilled in theart are accomplished by (a) using halogen-free hydrocarbon blowingagents or mixtures thereof and limiting the amount of hydrocarbonblowing agents with Lower Explosive Limit (LEL) values less than 2% inair in the formulation and (2) using a halogen-free flame retardant. Theterm “halogen-free” is defined herein as the property or condition of asubstance containing less than 0.3% of any halogen element such asfluorine, chlorine, bromine, or iodine.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 illustrates the layout for the insulation boards for the roofassembly for the FM 4450 calorimeter Test conducted on foams produced inExamples 8-13.

DETAILED DESCRIPTION OF THE INVENTION

It has unexpectedly been found that use of 1 or more less flammablehydrocarbon blowing agents (i.e., hydrocarbons with LEL values greaterthan 2%) and blends of such less flammable hydrocarbon blowing agentswith more flammable hydrocarbons (i.e., hydrocarbons with LEL valuesless than 2%) with non-halogen containing flame retardants in afoam-forming mixture is particularly advantageous because rigidpolyurethane foams that can withstand exposure to the 5000 Btu/minflaming heat source applied in E-84 testing to the extent that a Class Bdesignation can be obtained and that flammability criteria in FM 4450testing are met. The halogen-free rigid polyurethane foams produced inaccordance with the present invention can be made at lower density whilestill meeting the ASTM E-84 NFPA 101 Class B and passing the FM 4450Roof calorimeter test standards for roofing applications.

The present invention will now be described for purposes of illustrationand not limitation. Except in the operating examples, or where otherwiseindicated, all numbers expressing quantities, percentages,functionalities and so forth in the specification are to be understoodas being modified in all instances by the term “about”.

The foam-forming compositions of the present invention include:

-   -   a) at least 50% by weight based on total weight of the        foam-forming composition, of an organic polyisocyanate,    -   b) at least one isocyanate-reactive polyether or polyester        polyol with a nominal functionality of at least 2.0,    -   c) a hydrocarbon blowing agent mixture that includes:        -   i. no more than 10% by weight, based on total weight of the            foam-forming composition, preferably, no more than 8% by            weight, most preferably, from 2 to 8% by weight, of one or            more hydrocarbon compounds having individual LEL less than            2% by volume in air,    -   and/or        -   ii. one or more hydrocarbon compounds having an individual            LEL greater than 2% by volume in air,    -   and        -   iii. up to 1% by weight, based on total weight of the            foam-forming composition, of water,            and    -   d) at least one halogen-free flame retardant compound.

These compositions produce a polyurethane foam having a density rangingfrom 1.60 pcf (25.6 kg/m³) to 5 pcf (80.1 kg/m³) that meets the NFPA 101Class B ASTM E-84 standard and passes the FM 4450 Roof calorimeter testwhen reacted.

The LEL for a combustible gas is defined as the lowest concentration ofthat gas in air by volume that will ignite or catch fire in the presenceof an ignition source. Hydrocarbon gases commonly used to make PIR rigidfoam insulation include n-pentane, isopentane, and cyclopentane whichhave LEL values of 1.5%, 1.4%, and 1.1% at 20° C. and 1 atmosphere ofpressure, respectively.

The LEL value for any gas or vapor can be found in the Material SafetyData Sheets from the suppliers of that material or in referencematerials such as the NIOSH Pocket Guide to Chemical Hazards. The amountof these compounds used depends upon the desired foam density and mayrange from about 2% to 15% by weight, based on total weight of thesystem. Even though the blowing agent is only a small portion of thetotal foam-forming system, it exerts a disproportionate effect onflammability performance in tests where an ignition source is used inthe presence of a controlled draft such as in the ASTM E-84 Tunnel test.

In the present invention, the amount of extremely flammable material orcombination of materials with an LEL of less than 2% must be limited tono more than 10%, preferably, less than 8%, most preferably, from 2 to8% by weight, based on total weight of the foam-forming system. Examplesof suitable hydrocarbons having an LEL of less than 2% which aresuitable as blowing agents in the foam-forming reaction mixtures of thepresent invention include: n-pentane, isopentane, cyclopentane, butane,hexane, 2,2-dimethylbutane, 2-methylpentane, butenes, hexenes, andpentenes. The most preferred extremely flammable hydrocarbon compoundsare n-pentane, isopentane, cylcopentane and mixtures thereof with LELvalues less than 2%.

Some water is included in the foam-forming mixture in an amountnecessary to achieve the desired density as carbon dioxide generated byreaction of the water with the isocyanate acts as a co-blowing agent.

It is, of course, possible to use a combination of extremely flammablematerial(s) having an LEL of less than 2% with some amount of a slightlyless flammable material having an LEL greater than 2% by volume in air.The amount of the less flammable hydrocarbon will vary depending uponthe foam properties sought, e.g., density. Examples of suitablehydrocarbons having an LEL greater than 2% by volume in air include:acetone, acetaldehyde, dimethyl carbonate, dimethyl ether, methylal,ethyl formate, methyl acetate, and methyl formate. Methyl formate ismost preferred.

In addition to the hydrocarbon blowing agent, some water is included inthe blowing agent composition. The appropriate amount of water isdetermined on the basis of the desired foam density to be generated bythe carbon dioxide gas co-blowing agent.

The amount of water included in the foam-forming reaction mixture willgenerally range from about 0.05% to about 1% by weight, based on totalweight of the foam-forming system, preferably from about 0.10% to about0.80%, most preferably, from about 0.10% to about 0.40% by weight.

The blowing agent composition of the present invention reduces the needfor highly efficient vapor phase radical scavengers so that condensedphase flame retardants free of halogen can be used to produce Class Brigid foam systems.

For higher density foams (i.e., foams having a density of at least 1.80pounds per cubic foot (28.8 kg/m³), preferably, from 1.80 pcf (28.8kg/m³) to 5 pcf (80.1 kg/m³), most preferably, from 1.85 pcf (29.6kg/m³) to 3 pcf (48.1 kg/m³)) meeting the NFPA 101 Class B ASTM E-84standard and passing the FM 4450 Roof calorimeter test, the blowingagent composition need only include (i) up to 1% by weight, based ontotal weight of foam-forming system, preferably, from 0.10% to 0.80% byweight, most preferably, from 0.10% to 0.40% by weight, of water toproduce carbon dioxide (CO₂) as a co-blowing agent and (ii) less than10% by weight, based on total weight of the foam-forming composition,preferably, from 2% to 10% by weight, most preferably, from 2% to 8% byweight, of one or more hydrocarbon compounds having LEL values less than2%.

Generally, no hydrocarbon blowing agent with an LEL greater than 2% isrequired to prepare foams having densities greater than about 1.85 pcf(29.6 kg/m³) with a halogen-free flame retardant. However, inclusion ofa hydrocarbon blowing agent with an LEL greater than 2% in amounts of upto 5% by weight, based on total weight of foam-forming system is withinthe scope of the present invention. The optimum amount of hydrocarbonblowing agent with an LEL value of greater than 2% by volume in air toachieve a desired balance of flammability performance, thermalconductivity, compressive strength, and dimensional stability can bereadily determined by those skilled in the art.

For lower density foams at the higher end of the FSI Class B range(i.e.,foams having a density of less than 1.80 pcf (28.8 kg/m³), preferablyfrom 1.50 pcf (24 kg/m³) to 1.85 pcf (29.6 kg/m³), most preferably, from1.60 pcf (25.6 kg/m³) to 1.80 pcf (28.8 kg/m³)), the blowing agentcomposition used to produce foams in accordance with the presentinvention need only include (i) one or more hydrocarbon compounds havingan individual LEL less than 2% by volume in air and (ii) no more than 1%by weight, based on total weight of the foam-forming system, preferably,from 0.10% to 0.80% by weight, most preferably, from 0.10% to 0.40% byweight, of water. Although one or more hydrocarbons having an LEL valuegreater than 2% by volume in air may be included in the blowing agentcomposition for lower density foams in amounts of up to 5% by weight, itis preferred that no more than 2% by weight and most preferred that nohydrocarbon having an LEL value of greater than 2% by volume in air beincluded in such blowing agent composition.

For lower density foams with better flame spread performance(i.e., foamshaving a density of less than 1.80 pcf (28.8 kg/m³), preferably from1.50 pcf (24 kg/m³) to 1.85 pcf (29.6 kg/m³), most preferably, from 1.60pcf (25.6 kg/m³) to 1.80 pcf (28.8 kg/m³)), the blowing agentcomposition used to produce foams in accordance with the presentinvention need only include (i) one or more hydrocarbon compounds havingan individual LEL greater than 2% by volume in air and (ii) no more than1% by weight, based on total weight of the foam-forming system,preferably, from 0.10% to 0.80% by weight, most preferably, from 0.10%to 0.40% by weight, of water. Although one or more hydrocarbons havingan LEL value less than 2% by volume in air may be included in theblowing agent composition for lower density foams in amounts of up to 7%by weight, it is preferred that no more than 5% by weight and mostpreferred that no more than 2% of hydrocarbon having an LEL value ofless than 2% by volume in air be included in such blowing agentcomposition.

The optimum amount of hydrocarbon is dependent upon the LEL for thecompound or blend. Higher LEL values allow more blowing agent to be usedin rigid foam production to lower density or increase isocyanate index.

Any of the known polyfunctional isocyanates may be used in the practiceof the present invention. Examples of suitable polyisocyanates include:substituted or unsubstituted aromatic, aliphatic, and cycloaliphaticpolyisocyanate compounds having at least two isocyanate groups.

Polyfunctional aromatic isocyanates are particularly preferred formaking rigid polyurethane foam insulation. Examples of suitable aromaticisocyanates include: 4,4′-diphenylmethane diisocyanate (MDI), polymericMDI (PMDI), toluene diisocyanate, allophanate-modified isocyanates,isocyanate-terminated prepolymers and carbodiimide-modified isocyanates.Polymeric MDI having an average NCO functionality of from 2.2 to 3.3 anda viscosity of from 25 to 2000 mPas and prepolymers of such polymericMDI prepared with polyols or other oligomers or polymers such aspolyether or polyester polyols that contain active hydrogen atoms. Themost preferred PMDI has a functionality of from 2.2 to 3.0 and aviscosity less than about 800 mPas at 25° C. The organic polyisocyanateused in the foam-forming system of the present invention may, of course,be a mixture of such polyisocyanates.

The organic polyisocyanate(s) is/are included in the foam-forming systemin an amount of at least 50%, preferably, from about 55% to about 75%,most preferably, from about 55% to about 67% by weight, based on totalweight of the foam-forming system.

Any material having at least two reactive groups capable of reactingwith an isocyanate group is suitable for use in the polyurethane-formingreaction mixtures of the present invention. Particularly preferredisocyanate-reactive materials include polyester and polyether polyolshaving at least two isocyanate-reactive end groups, preferably, from 2to 8 isocyanate-reactive end groups, most preferably, from 2 to 6isocyanate-reactive end groups and blends thereof are particularlysuitable for the practice of the present invention. Aromatic polyestersare most preferred because of their generally higher thermo-oxidativestability. Examples of commercially available polyester polyols suitablefor use in the practice of the present invention are those sold by theStepan Company under the name Stepanpol and those sold by Invista underthe name Terate. Polyester or polyether polyols that contain halogenatedflame retardants or additives are not suitable for use in thehalogen-free reactive systems and foams of the invention. Preferredpolyols for use in the present invention will generally havefunctionalities of from 2.0 to 8.0 and hydroxyl numbers of from about 25mg KOH/gm to about 1000 mg KOH/gm. More preferred are aromatic polyesterpolyols having hydroxyl numbers from about 100 mg KOH/gm to about 500 mgKOH/gm and functionalities of from 2.0 to about 2.5. Most preferred areblends of aromatic polyester polyols and polyester or polyether polyolsthat contain renewable content derived from incorporation of regenerablematerials such as fatty acid triglycerides, sugars, or natural glycerin.

The polyol(s) is/are generally included in the foam-forming reactionmixture in an amount of from 10% to 45%, preferably, from 20% to 40%,most preferably, from 25% to 40% by weight, based on total weight of thefoam-forming mixture.

Hydrocarbon blowing agents are used in the reactive systems of thepresent invention. The term hydrocarbon is used herein to refer tochemical compounds composed primarily of carbon and hydrogen that maycontain heteroatoms such as oxygen, nitrogen, sulfur, or other elementsexcluding halogens. Halogenated blowing agents are not used in thepractice of the invention. For purposes of description of the invention,extremely flammable hydrocarbon blowing agents are defined as compoundswith LEL values less than 2% by volume in air and include n-pentane,isopentane, cyclopentane, butane, hexane, 2,2-dimethylbutane,2-methylpentane, butenes, hexenes, and pentenes. The most preferredextremely flammable hydrocarbon compounds are n-pentane, isopentane,cylcopentane or mixtures thereof with LEL values less than 2% thatcomprise less than 10% based on total system weight of the totalreaction system. Formulation compositions comprised of less than 8% byweight on total system weight of extremely flammable hydrocarbon blowingagents are even more preferred.

Slightly less flammable hydrocarbon compounds with LEL values equal toor greater than 2.0% by volume in air may be used in combination withextremely flammable blowing agents or used alone to further reduceflammability of the blowing agent mixture and/or produce rigidpolyurethane materials with densities less than 1.85 lbs./ft³(29.6kg/m³). Less flammable hydrocarbon blowing agents with LEL valuesgreater than or equal to 2.5% such as acetone, acetaldehyde, dimethylcarbonate, dimethyl ether, methylal, ethyl formate, methyl acetate, andmethyl formate are preferred in the practice of this aspect of theinvention with methyl formate being most preferred as the slightly lessflammable hydrocarbon blowing agent.

Water also may be used in the practice of the invention to furthercontrol product density since it reacts with isocyanates to producecarbon dioxide gas as an auxiliary blowing agent. However, the thermalconductivity of CO₂ is generally higher than those of hydrocarbonblowing agents, so the amount of water in the formulation must becontrolled to prevent negative effects on the insulating ability ofrigid foam produced by the practice of the invention. Consequently, nomore than 1% by weight of water based on total system weight is used inthe reactive system and levels less than 0.8% are preferred in thepractice of the invention.

Only halogen-free flame retardants are suitable for use in the reactivesystems of the present invention. Suitable flame retardants may benonreactive or reactive solids or liquids at normal temperatures andpressures. Halogen-free flame retardants, as that term is used herein,includes any compounds other than isocyanate-reactive materials thatcontain only carbon, hydrogen, oxygen and/or nitrogen that demonstrate ameasurable improvement in flammability performance in ASTM E-84 whencompared to the same reactive system without the flame retardantcompound present. Suitable solid flame retardants include ammoniumpolyphosphates, melamine and its derivatives, borates, aluminumtrihydrate (ATH), magnesium hydroxide, silicates, graphite, and nanoclayparticles. However, liquid halogen-free flame retardants are preferredbecause equipment modifications are generally not required. Desirablehalogen-free liquid flame retardants include halogen-freeorganophosphorus and silicone compounds. Suitable organophosphoruscompounds include: phosphates, phosphonates, phosphites, phosphineoxides, phosphorus derivatives of iscyanate reactive materials such asdiethyl N,N′-bis(2-hydroxyethyl) aminomethyl phosphonate and phosphateesters of the Exolit OP 500 series. Triethyl phosphate, tributylphosphate, tributoxyethyl phosphate, oligomeric ethyl ethylenephosphate, bisphenol A bis(diphenyl phosphate), resorcinol bis(diphenylphosphate), diethyl ethyl phosphonate, and dimethyl propane phosphonateare preferred organophosphorus compounds for practice of the invention.

Other additives known to be useful in the production of rigid foams suchas surfactants, catalysts, processing aids, chain extenders, andcross-linkers may be added to the reactive systems of the presentinvention. Surfactants are generally copolymers of ethyleneoxide/propylene oxide with polysiloxanes that control nucleation andcell-size distribution in the rigid foam and improve mixing of the blendcomponents. Some of the commercially available surfactants include thoseof the Tegostab® series from Evonik such as Tegostab® 8513 and Tegostab®8465. Amine catalysts promote reaction of active hydrogen compounds suchas polyols and water with isocyanates and may, along with metalcarboxylates, trimerize isocyanate groups into highly thermally stableisocyanurate linkages. Pentamethyldiethylenetriamine (PMDETA),dimethylcyclohexylamine, and tris 2,4,6-dimethylaminomethyl phenol areexamples of suitable amine catalysts. Potassium octoate and acetate areexamples of suitable metal carboxylate trimer catalysts.

Suitable amounts of such additives to be included in the foam-formingsystem of the present invention may be readily determined by thoseskilled in the art.

Foams meeting the NFPA 101 Class B ASTM E-84 standard and passing the FM4450 Roof calorimeter test are produced by reacting the organicpolyisocyanate and the isocyanate-reactive composition in the presenceof a halogen-free hydrocarbon blowing agent and optionally, water. Anyof the known techniques for producing a rigid polyurethane foam may beused.

The foams of the present invention are characterized by an NFPA 101Class B rating measured in accordance with ASTM E-84 standard and bymeeting the flammability criteria for an FM 4450 Class 1 rating. Thesefoams are particularly useful for insulation applications and roofingassemblies.

Processes for producing foams from the foam-forming compositions of thepresent invention are known to those skilled in the art. Examples ofsuitable processes include the known methods for producingpolyisocyanurate laminated board stock insulation, methods for producingfree-rise bunstock rigid foam insulation, froth-forming method forcontinuously producing glass fiber reinforced insulation boards inaccordance with teachings of U.S. Pat. No. 4,572,865, continuous ordiscontinuous methods.

EXAMPLES

The present invention is further illustrated, but is not to be limited,by the following examples in which all parts and percentages are partsby weight or percentages by weight, unless otherwise indicated.

Characteristics and flammability test results for foams prepared fromthe foam-forming systems of the present invention are reported in theTables. All ASTM E-84 (UL 723) tunnel tests were done on 2.75″ (7 cm)thick samples without facer at Underwriters Laboratories Northbrook,Ill. facility while FM 4450 calorimeter tests were done on nominal 1.5″(3.8 cm) thick samples with facer. Thicker samples typically producemore smoke and higher flame spread in the tunnel and thinner samples aremore likely to fail the calorimeter test. It is particularly noteworthythat inventive Example 13 made with 100% pentane as a blowing agent andinventive Example 10 made with an 80/20 blowing agent blend of pentaneand methyl formate performed so poorly relative to the halogenatedcontrol comparative Example 8 in the predictive lab muffle furnace test.However, both samples easily passed the full-scale FM 4450 Roofcalorimeter test. This observation supports the performance requirementthat rigid foams of the invention with a Class B rating must pass theFactory Mutual test since smaller scale test results may be misleading.

Hand-Mix Lab Foam Preparation Procedure

All B-side components (i.e., components included in theisocyanate-reactive component) with the exception of the blowing agentwere blended with a mechanical flat blade turbine mixer. Blowing agentwas added to the B-side resin blend and mixed briefly before theisocyanate was added and the resultant mixture was mixed at high speedfor about 5 seconds. The mixture was then poured into a 12″ (30.5cm)×12″ (30.5 cm)×2.5″ (6.4 cm) cardboard box and the foam was allowedto rise freely. The rising foam surface was gently probed with a woodenstick to determine string gel and tack free time. In instances where asample was needed to perform the Bayer Mini Tunnel Test (describedbelow), the foam mixture was poured into two 14″ (35.6 cm)×6⅜″(16.2cm)×4″ (10.2 cm) cardboard boxes so that four 12″ (30.5 cm)×6⅞″ (17.5cm)×1″ (2.5 cm) samples could be cut from the foam cores.

Bayer Alpha Mini Tunnel Test

Performance in this small scale tunnel test roughly correlates toresults obtained in the Steiner Tunnel used to conduct ASTM E-84testing. Core foam samples are cut to 6⅞″ (17.5 cm)×48″ (121.9 cm)×up to2″ (5.1 cm) thick. Multiple foam samples of equal length can be used fora total length of 48 inches (121.9 cm). Typically three sample sections16 inches (40.6 cm) long are used to simulate the three 8′ (243.8 cm)long samples in the full scale test. The sample sections are placed inthe tunnel and ignited by the burner that is positioned such that theflame tip is 14″ (35.6 cm) from the start end of the tunnel. Progressionof the flame from the burning foam along the tunnel is recorded at timedintervals by an operator observing through windows installed in thetunnel “floor”. The operator actually monitors the flame by looking atthe flame reflection in an angled mirror positioned underneath clearwindow “floor” of the raised tunnel apparatus. An optical sensor in thetunnel ventilation system gathers data that is used to calculate thesmoke index. The Flame Spread Constant of a 48 inch (121.9 cm) sample(FSC₄₈) is calculated using the following equation:

$\frac{{{Average}\mspace{14mu}{Distance}} - {14}}{{FSC}_{48}} = \frac{29.9 - 14}{22}$

Based on historical comparisons of results obtained for samples testedin both the Steiner Tunnel and the Bayer Alpha Mini Tunnel, a FSC₄₈ of28 or less and a smoke index of 200 or less is expected to correspond toan E-84 flame spread index of 25 or less with a smoke index of 450 orless. The alpha tunnel test does not correlate well with foam sampleshaving a flame spread index (FSI) greater than 35 in the large scaleASTM E-84 tunnel test since the flame spread of such foams usuallyexceeds 48 inches (121.9 cm) in the lab tunnel.

Bayer Muffle Furnace Test

This test was designed to compare behavior of test materials to that ofcontrols that are known to pass requirements of the Factory Mutual Roofcalorimeter test (FM 4450). A foam sample with dimensions of 4″ (10.2cm)×4″ (10.2 cm)×up to 2.5″ (6.4 cm) was completely wrapped in aluminumfoil. The mass of the foil and foam were recorded separately along withthe foam height. A small muffle furnace containing a removable open topmetal compartment sized to hold the foam sample was preheated to 450° C.The oven was opened briefly to insert the foil-wrapped foam sample intothe metal holder and the foam was heated for 20 minutes at 450° C. Themetal holder was removed from the oven and allowed to cool. The weightof foil-wrapped foam sample was recorded before gently un-wrapping thefoam to measure and record its residual height at the sample's thinnestsection of remaining foam. Also, the height of any foam area free ofchar was recorded. Test results are reported as % weight lost, % heightretained, and the amount of “no char” in inches. The results arecompared to those of a control sample that is known to pass the Roofcalorimeter test with the expectation that the experimental sample willpass also if its results are equal to or better those of the control.However this assumption typically is only valid for samples prepared viaa high-pressure mixing machine process as would be used to make thecommercial product. As illustrated in Table 2, muffle furnace resultsfor hand-mixed lab foams can differ markedly from those obtained usingthe same formulation on the laminator machine.

Pilot Line Laminator Unit

PIR laminated boardstock foam samples were prepared on Bayer'spilot-scale Hennecke unit at the Pittsburgh, Pa. USA facility. Thelaminator was approximately 26 feet (7.9 m) long and equipped with asingle mix-head which made boards that were 30 inches (76.2 cm) wide.The mix-head was outfitted with a two-stream “T” made with CPVC piping.The B side resin blend (i.e., polyol-containing component) was premixedwith the third-streamed blowing agent inline via a special Triple ActionDispersion Device (TADD) from Komax, Inc. prior to entering the staticmixer and exiting the mix-head after being subjected to impingementmixing at 1800 psi (126.6 kg/cm²) to 2500 psi (175.8 kg/cm²). Theconditions used for foams made in this study were as follows:

Total Feed Rate  22 to 45 lbs./min (10-20.4 kg/min) Resin Temperature 82° F. Isocyanate Temperature  82° F. Platen Temperature 145° F. LineSpeed  34 to 38 ft./min (10.4-11.6 m/min)The nominal board thickness for tested foams in Table 3 was set at 1.5inches (3.8 cm) unless otherwise noted and the foam was laminated withblack facer. The board was perforated on the top surface using aweighted spiked roller as it exited the unit.ASTM E-84 (UL 723) Tunnel Testing

All foam samples for this test were prepared at a nominal thickness of3.0″ (7.6 cm) with standard black facer. The top and bottom ¼″ (0.6 cm)of foam was slit from the boards to remove the facer. The slit sampleswere tested at Underwriters Laboratories Fire Protection facilities inNorthbrook, Ill. as developmental materials.

Roof Assembly for FM 4450 calorimeter Test

The roof assembly was built by personnel at Factory Mutual's testlaboratory in West Glocester, R.I. and was composed of the followinglayered sequence:

-   -   1. Approved 18 gauge steel deck.    -   2. Rigid foam roof insulation samples with standard black facer,        mechanically attached to the deck.    -   3. 3 ply organic felt Built-Up roof with hot asphalt applied at        25 lbs. per 100 square feet (1.22 kg/m²).    -   4. 60 lb. (27.2 kg) flood coat of asphalt.

The layout for installation of these roof insulation boards was slightlydifferent from the conventional diagram based on 48-inch (122 cm) widecommercial product and is shown in FIG. 1. In the conventional assembly,a 36-inch (91.4 cm) wide panel and 24-inch (61 cm) wide panel form asingle vertical seam in the assembly, but the installation used fortesting of roofing assemblies made with the foams of the presentinvention required that two vertical seams using two 24-inch (61 cm)wide boards and a single 12-inch (30.5 cm) wide panel be used becausethe pilot laminator unit could only make boards with a maximum width of30 inches (76.2 cm). No thermal barrier was used between the deck andfoam insulation and no cover board was used on top of the foaminsulation.

Various formulations used to prepare rigid polyurethane foams based onthe inventive reactive systems are shown in Tables 1, 2 and 3. Theamounts listed in Tables 1, 2 and 3 are parts by weight.

The materials used to produce the foams in the Examples which followwere:

-   POLYOL: Stepanpol® PS-2352 polyester polyol having a functionality    of 2 and an OH Value of 235 which is commercially available from the    Stepan Company.-   K-15: Potassium octoate which is commercially available under the    name Dabco® K-15 from Air Products Company,-   PMDETA: pentamethyldiethylenetriamine available under the name    Desmorapid® PV from Bayer MaterialScience.-   Polycat 46: Potassium acetate available under the name Polycat® 46    from Air Products Company.-   B 8513: Surfactant available under the name Tegostab® B 8513 from    Evonik Industries.-   PCF: Halogenated flame retardant which is commercially available    under the name Fyrol® PCF from ICL-Supresta.-   TEP: Halogen-free flame retardant triethyl phosphate commercially    available from Eastman Chemical.-   TEP-Z: Halogen-free flame retardant commercially available under the    name Levagard® TEP-Z available from Lanxess.-   RDP: Resorcinol bis(diphenyl phosphate), halogen-free flame    retardant which is commercially available under the name Fyrolflex®    RDP from ICL-Supresta,-   n-Pentane: The blowing agent n-pentane.-   MF: The blowing agent methyl formate.-   NCO: Polymeric MDI which is commercially available under the name    Mondur® 489 from Bayer MaterialScience.

TABLE 1 Hand-Mixed Foams Example 1 2 3 POLYOL 29.55  27.42 33.00 TEP2.25 — 3.50 RDP — 3.56 — B 8513 0.72 0.54 0.76 K-15 1.44 1.19 1.06Polycat 46 0.23 0.23 — PMDETA 0.11 0.21 0.08 Water 0.22 0.10 0.15n-Pentane 5.61 6.75 6.47 NCO 60.3 60.0 55.0 Index 2.75 2.75 2.50 Density(pcf) 1.75 1.76 1.73 [kg per m³] [28]    [28.2] [27.7] Mini Tunnel FSC37    38 — SDI 218    170 —

TABLE 2 Muffle Furnace Results: Hand-Mix vs Machine (Laminator) Example4* 5* 6* 7* Hand-mix Hand-mix Laminator Laminator POLYOL 28.00 28.0028.08 28.08 PCF 3.70 3.70 3.71 3.71 B-8513 0.70 0.70 0.70 0.70 K-15 1.421.42 1.42 1.42 Polycat 46 0.22 0.22 0.22 0.22 PMDETA 0.11 0.11 0.12 0.12Water 0.14 0.14 0.14 0.14 n-pentane 6.12 6.12 6.02 6.02 NCO 59.58 59.5859.58 59.58 Index 3.00 3.00 3.00 3.00 Density (pcf) 1.75 [28]  1.75[28]   1.71 [27.4]  1.74 [27.9] [kg/m³] Thickness, 1.99 [5.1] 1.48 [3.8]2.18 [5.5] 1.64 [4.2] Initial (in.) [cm] Muffle Furnace Height, % 83 8157 47 Retention Weight, % 37 37 44 46 Lost No Char (in.) 0.65 [1.7] 0.44[1.1] 0.61 [1.5] 0.30 [0.8] [cm] *Comparative Example

TABLE 3 Laminator Board Samples Example 8* 9 10 11 12 13 POLYOL 28.0429.47 29.14 29.07 28.40 33.00 PCF 4.01 — — — — — TEP — 2.25 3.55 — —3.50 RDP — — — 3.58 5.62 — B 8513 0.70 0.72 0.71 0.71 0.70 0.76 K 151.42 1.42 1.41 1.42 1.42 1.06 Polycat 46 0.22 0.23 0.23 0.23 0.23 —PMDETA 0.11 0.11 0.11 0.11 0.11 0.08 Water 0.14 0.22 0.22 0.22 0.21 0.15n-Pentane 5.88 4.21 4.11 4.23 4.14 6.47 MF — 1.05 1.03 1.06 1.03 — NCO59.5 60.3 59.5 59.4 58.1 55.0 Index 3.00 2.75 2.75 2.75 2.75 2.50Density (pcf) [kg/m³] 1.73 [27.7] 1.78 [28.5] 1.78 [28.5] 1.79 [28.7]1.71 [27.4] 1.67 [26.8] Bd. Thickness (in.) 1.67 [4.2] 1.64 [4.2] 1.62[4.1] 1.65 [4.2] 1.69 [4.3] 1.70 [4.3] [cm] Compressive Strength 14.6[1] 14.4 [1] 17.0 [1.2] 18.8 [1.3] 16.1 [1.1] 15.8 [1.1] 10% Defl. (psi)[kg/cm²] Init. K-factor @ 35° F., 0.158 0.157 0.154 0.156 0.157 0.161Btu-in./hr.ft²° F. Mini Tunnel FSC 33 34 34 35 32 33 SDI 107 206 195 172131 97 Muffle Furnace Height, % Retention 49.7 2.4 2.5 68.6 71.5 10.2Weight, % Lost 48.8 52.6 50.3 49.0 49.1 52.0 No Char (in.) [cm] 0.145[0.37] 0 0 0.495 [1.26] 0.385 [1] 0 ASTM E-84 Thickness (in.) [cm] —2.75 [7] — 2.75 [7] 2.75 [7] 2.75 [7] Density (pcf) [kg/m³] — 1.71[27.4] — 1.75 [28] 1.71 [27.4] 1.54 [24.7] FSI — 45 — 40 35 65 SDI — 170— 145 150 195 NFPA 101 Rating — Class B — Class B Class B Class B FMCalorimeter Fuel Contribution Rates BTU/ft.²/min. Pass — Pass Pass PassPass 3 min. (410 max) 190 — 207 89 118 246 5 min. (390 max) 190 — 207 89117 244 10 min. (360 max) 159 — 205 89 117 243 30 min. Avg. (285 133 —154 87 87 167 max) *Comparative Example

The foregoing examples of the present invention are offered for thepurpose of illustration and not limitation. It will be apparent to thoseskilled in the art that the embodiments described herein may be modifiedor revised in various ways without departing from the spirit and scopeof the invention. The scope of the invention is to be measured by theappended claims.

What is claimed is:
 1. A polyurethane foam comprising the reactionproduct of a polyurethane foam-forming composition consisting of: a) atleast 55% by weight based on total weight of foam-forming composition ofan organic polyisocyanate, b) at least one polyether polyol or polyesterpolyol with a nominal hydroxyl functionality of at least 2.0, c) 4.11 to8% by weight, based on total weight of foaming-forming composition, of apentane selected from n-pentane, isopentane, cyclopentane or a mixturethereof, d) 0.21 to 0.40% by weight, based on total weight offoam-forming composition, of water, e) triethyl phosphate or resorcinolbis(diphenyl phosphate), f) one or more catalysts, g) a polyetherpolysiloxane copolymer, and h) optionally one or more of a chainextender and a cross-linker, wherein the polyurethane foam has a densityof less than 1.8 pounds per cubic foot, a flame spread index of 26 to 75according to ASTM E-84, and passes an FM 4450 Calorimeter Test.
 2. Thepolyurethane foam of claim 1, wherein the organic polyisocyanatecomprises polymeric MDI and is present in an amount of 55% to 67% byweight, based on the total weight of the foam-forming composition. 3.The polyurethane foam of claim 1, wherein the foam has isocyanuratelinkages.
 4. An insulated roof assembly comprising: (a) a deck; (b)insulation panels mechanically attached to the deck, wherein theinsulation panels comprise the polyurethane foam of claim
 1. 5. Thepolyurethane foam of claim 1 having a flame spread index of 35 to 65according to ASTM E-84.
 6. The polyurethane foam of claim 1 wherein theone or more catalysts consist of an amine catalyst and a metalcarboxylate trimer catalyst.
 7. The polyurethane foam of claim 1 whereinthe pentane comprises n-pentane.
 8. The polyurethane foam of claim 1,wherein the pentane consists of n-pentane.
 9. A polyurethane foamcomprising the reaction product of a polyurethane foam-formingcomposition consisting of: a) at least 55% by weight based on totalweight of foam-forming composition of an organic polyisocyanate, b) anisocyanate reactive composition comprising at least one polyether polyolor polyester polyol with a nominal hydroxyl functionality of at least2.0, c) 6.47 to 8% by weight, based on total weight of foaming-formingcomposition, of a pentane selected from n-pentane, isopentane,cyclopentane or a mixture thereof, d) 0.15 to 0.40% by weight, based ontotal weight of foam-forming composition, of water, e) triethylphosphate or resorcinol bis(diphenyl phosphate), f) one or morecatalysts, g) a polyether polysiloxane copolymer, and h) optionally oneor more of a chain extender and a cross-linker, wherein the polyurethanefoam has a density of less than 1.8 pounds per cubic foot, a flamespread index of 26 to 75 according to ASTM E-84, and passes an FM 4450Calorimeter Test.
 10. The polyurethane foam of claim 9, wherein theorganic polyisocyanate comprises polymeric MDI and is present in anamount of 55% to 67% by weight, based on the total weight of thefoam-forming composition.
 11. The polyurethane foam of claim 9, whereinthe foam has isocyanurate linkages.
 12. An insulated roof assemblycomprising: (a) a deck; (b) insulation panels mechanically attached tothe deck, wherein the insulation panels comprise the polyurethane foamof claim
 9. 13. The polyurethane foam of claim 9 having a flame spreadindex of 35 to 11 according to ASTM E-84.
 14. The polyurethane foam ofclaim 9 wherein the one or more catalysts consist of an amine catalystand a metal carboxylate trimer catalyst.
 15. The polyurethane foam ofclaim 9 wherein the pentane comprises n-pentane.
 16. The polyurethanefoam of claim 9, wherein the pentane consists of n-pentane.